// ml:run = $bin < input
#include <iostream>
#include <cmath>
#include <iomanip>

long double const eps = 1e-7;
long double yy1, yy2, yw, xb, yb, r;
long double x;

long double dis(long double x1, long double yy1, long double x2, long double yy2)
{
    /* std::cerr << x1 << " " << yy1 << " " << x2 << " " << yy2 << "\n"; */
    return std::sqrt((x1 - x2) * (x1 - x2) + (yy1 - yy2) * (yy1 - yy2));
}

bool work(long double y0)
{
    long double k = (yw - yb - r) / (yw - y0 - r);
    x = xb / (k + 1.0);
    if (x >= xb) return false;
    long double d = (yy2 - y0) * x / dis(0, y0, x, yw - r);
    /* std::cerr << d << "\n"; */
    return d >= r + eps;
}

int main()
{
    std::ios_base::sync_with_stdio(false);
    std::cin >> yy1 >> yy2 >> yw >> xb >> yb >> r;
    if (work(yy1 + r)) {
        std::cout << std::fixed << std::setprecision(10) << x << "\n";
        return 0;
    }
    std::cout << "-1\n";
}

